Arrangement for prevention of corrosion in precipitators



Aug. 21, 1951 A. u. wAsTvlND ET Ax.

ARRANGEMENT FOR PREVENTION OF' CORROSION IN PRECIPITATORS Filed Sept. l1, 1946 S n R 10. o n .m r V E e V d QW\\\Q\\\\%Q h N n a .n m` .I I .AN V W` \m\\ P O m .l a W l... H ,n r a a H KA @www Attorney.

Patented Aug. 21, 1951 ARRANGEMENT FOR PREVENTION OF CORROSION IN RECIPITATORS Allan Uno Wstvind, Abrahamsberg, and Karl Harry Andersson, Stockholm, Sweden, assignors to A. B. Svenska Flaktfabriken, Stockholm,

Sweden Application September 11, 1946, Serial N0. 696,180 In Sweden June 12, 1945 (Cl. 18S-'7) 4 Claims.

Serious corrosion problems appear often in factories during suspension of operation. These problems are particularly troublesome for machines, specially apparatus operating with gases containing -condensable vapours flowing therethrough as for instance apparatus for purifying combustion gases, in the following description termed electrolters. Such last mentioned gases often contain particles in a solid or liquid state which at a temperature lower than normal attack the material of the apparatus. rIhe difficulties not only aris-e after stopping the machines and during the time they are standing still but when they are to be restarted.

The present invention has for its object to eliminate corrosion of the material in machines, when out of operation, which machines use gases of the kind referred to as a drying medium by raising the temperature of the machine or a vulnerable part of the machine, to be protected,

vby supplying heat to such an extent, that the temperature reaches a point above the dew-point of the enclosed gas, preferably a point at which the moisture of the encl-osed gas does not act corroding in the presence of salts.

Arrangements for practicing the invention will be clear from the following description and the attached drawings, wherein the figure is a vertical section through an embodiment of the invention applied to an electrofilter.

Referring to the drawing, I designates a housing of an electrofilter e. g. for purifying of combustion gases from the smelting furnace of a sulphate pulp process. The lter housing is divided into two chambers 2 and 3, by means of a partition 3a. Inlet channels I and outlet channels 5 are in communication with the chambers, In the inlet as well as in the outlet channels dampers 6 are provided by means of which the chambers 2 and 3 may be shut off. A connecting channel 1, provided with a damper 8, is arranged between the inlet channels 4. In the same manner there is a connecting channel 9 between the two outlet channels 5. The channel 9 is to be shut oi by slide-shutters I0. A fan II and a heater I2 are arranged in the channel 9. The heater preferably is made to be heated electrically.

In order to reduce the relative humidity of the air in the electrofltter, the air circulating system preferably may be provided with a Ventilating fan I3 which by means of a pipe I4 forces air into the system so that the pressure in the system will be higher than the atmospheric pressure. The air, blown into the system, escapes through clearances round the dampers in the inlet and outlet channels respectively. If required the Ventilating air may be dehumidied by an apparatus I5. The dehumidicati-on may preferably be done by aid of silica gel 0r another similar material. This arrangement has the advantage that water vapour from the outside is prevented from entering the system and that water vapour eventually remaining in the system after stopping the machine may be ventilated out.

The function of the apparatus is the following. When the electrolter is brought out of operation the d-arnpers 6 are shut off and the damper 8 is opened as well as the slide-shutters I. An air-passage thus is provided permitting air to be circulated by aid of the fan l I from the chamber 2 through the channel 9 into the chamber 3 and from there through the channel l back to the chamber 2. The circulating air is heated by the heater I2 to a desired temperature which for an electrofilter preferably is 100 to 140 C. The temperature is preferably adapted to be regulated automatically to prevent excessive rise of temperature.

By maintaining the temperature of the appa- 1 ratus at a desired point during the time when the filter is out of normal operation the advantage is obtained that the lter is protected against corrosion and is permanently ready for restarting. If the electrolter is cold at starting it must be started without voltage until it has been heated up so much that its high tension insulators, which are in communication with the hot humid gas, have become warm enough so that condensation on them and as a result thereof discharge of electricity cannot occur. As soon as the insulators are warm enough to prevent condensation on them the electrical current is closed.

In smaller apparatus it is not necessary to arrange comp-ulsory circulation of the gas but it is sufficient to provide the apparatus with heaters only which operate according to the thermosyphon principle.

The arrangements above described may of course be varied in several ways without departing from the scope of the present invention.

Having now described our invention, what we claim as new and desire to secure by United States Letters Patent is:

1. In an electrolter apparatus: a casing for housing an electrofilter, said casing being provided with inlet and outlet for a gas medium, means for shutting off said inlet and outlet, a partition in said casing dividing the lcasing lengthwiseA in the direction of ow, circulating openings in said partition adjacent the ends thereof, a

3 heater and a fan in one of said circulating openings, and means for closing said circulating openings to prevent passage of gas therethrough during the normal operation of the electrolter.

2. An apparatus as specied in claim l including meansV for closing one of said circulating openings to close 01T access to the heater and fan during normal operation of the electrolter.

3. An apparatus as specified in claim 1 providing a blower connected to said casing for introduction of outside air to maintain a pressure in the casing above atmospheric.

4. An apparatus as specified in claim 3 having drying means in series with said blower.

ALLAN UNO WSTVIND. KARL HARRY ANDERSSON.

l@ REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,391,436 Welch Sept. 20, 1921 1,922,125 Crowder Aug. 15, 1933 1,951,867 Grilli Mar. 20, 1934 2,215,267 Hedberg et al Sept. 17, 1940 FOREIGN PATENTS Number Country Date 278,396 Great Britain Oct. 12, 1927 

